This invention relates to a rotary anode for an X-ray tube, more specifically to an improvement of an intermediate layer or a bonding layer to bond an anode body to a target layer of such rotary anode.
X-ray tubes, especially those for medical application, have a rapidly rotating rotary anode formed of tungsten and a cathode facing opposite to the anode within a glass envelope kept under high-degree vacuum. The target layer formed over a target area of the rotary anode is bombarded with electron beams emitted from the cathode, and consequently the target layer emits X-rays.
Rotary anodes with large thermal capacities allow good heating radiation, thereby providing a large X-ray output.
Since molybdenum has larger thermal capacity and lower specific gravity as compared with tungsten, such rotary anodes composed of a laminate of molybdenum and tungsten layers are known. Also, there have been proposed rotary anodes comprising a graphite anode body to which there is bonded a target layer formed of tungsten or tungsten-rhenium alloy. Such rotary anodes are advantageous because graphite has larger thermal capacity as compared with tungsten and molybdenum. The defective point, however, is that tungsten and graphite would react to each other to form a brittle intermediate layer, thereby deteriorating the rotary anode.
U.S. Pat. No. 3,579,022 issued on May 18, 1971 entitled "Rotary anode for X-ray tube" eliminates the above defect by bonding the graphite anode body with the tungsten-rhenium alloy target layer by means of an intermediate layer of rhenium. In this U.S. patent the target layer and intermediate layer are both formed by taking advantage of the thermal decomposition of corresponding metal compounds.
The Japanese Patent application first disclosed under No. 79289/75 issued on June 27, 1975, assigned to the assignee of the present invention, is intended as an improvement of the aforesaid U.S. Pat. No. 3,579,022. According to this Japanese patent application, the anode body of graphite and the target layer of tungsten or its alloy are bonded by means of an intermediate layer of molybdenum or molybdenum-ruthenium alloy, and intermediate layer being formed by applying to the target area of the anode body a paste containing molybdenum powder or a paste containing molybdenum powder and ruthenium powder, laying a preformed tungsten sheet or band on the applied layer, and then hot-pressing the resultant laminated body under vacuum or in an inert gas.